Step 5: Machining the Housing

This is yet another step where I assume some knowledge of milling machine techniques.

I used a 1/8 inch end mill to machine 70 mil deep channels across the length of the housing. This provides heat sinking and more than doubles the thermally emissive surface area of the housing. The channels were cut front to back with respect to direction of travel of the bike. This allows the airflow from riding to dissipate the heat better. Cross cutting in the other direction resulting in a checker board pattern would increase turbulence and potentially increase cooling effectiveness. I have found though that after my 15 minute commute on cool evenings that the housing is just barely warm to the touch.

There are some excellent comments below regarding the coating of the housing. It turn out that for an application where convective airflow is the dominant cooling mechanism (as is the case here) that coating the surface of the aluminum will not measureably improve its heatsinking performance. In any case I decided to powder coat mine for durability and aesthetics. As stated above, the cooling performance of the housing is sufficient, so overall it seems to be working fine.

I will be uploading the diagram as soon as I get it done, sorry for any inconvenience :(

4 years later ... :)

OOPS :) <br> <br>4 years later I'm still using the headlight almost every day. Do you need any specific information that isn't here? I don't recall what diagram I was referring to, but if you need any pointers I can try.

&quot;I swear Officer, i Didn't See him&quot; <br>wouldn't be an acceptable excuse in this case XD

Looks like the store you got the LED's from might be out of business.

Great project. I'm a cyclist and I find the commercial BLTs etc are too bright when riding towards them. Much brighter than cars! I know they're great off-road but they're a bit antisocial on bike paths. I think dipping lights should be the next development, just as on cars. Maybe you have to go for reflectors and rear-pointing bulbs? I am going to give it a go.

i would like to make something like this for my motorbike, running it off the bikes battery. could it be done?? thanks crunchie

Sure!

I just ordered my Cree leds for an old overhead projector I'm converting to video.
Instead of the thermal epoxy, will regular thermal grease work if I used screws to hold the leds down? because I might use the leds for a different project later and be able to swap them out.

That should work fine. You can probably get away without thermal compound, but it can't hurt to add it assuming it is a thin layer (1-3 mils)

Alright, cool. Just got my lens, drivers and holders in the mail, just waiting for the LEDs now.
And as for a power supply, would a laptop charger at 15V 4 Amps work ok even though its built for (either lithium or polymer) ion batteries? Because I have a couple lying around the house and there not being used since the laptops have been recycled.

That sounds okay. I would think that the charging circuit is probably contained within the laptop or the battery itself. You could check by putting a voltmeter on the output of the power suppyl and just checking to see if 15 volts is present. 15V at 4 amps should be sufficient for a bunch of LEDs. Remember though that when using a boost (or buck) converter, the difference in the supply voltage to the converted voltage has a lot to do with determining the efficiency of the conversion, and that any inefficiency is turned into heat within the converter. So if you are boosting up to 21 volts (for 6 LEDs running at 1 amp) then you have a 6 volt difference which may be too large (check with the manufacturer of the converter) or it may be fine.

I am only going to put around 5 LEDs, give or take an LED, for each of the 3 series I am making. I am going to use copper caps that match the diameter, or a bigger cap, and use aluminum soda cans to dissipate the heat more, if needed since I do not have access to a milling machine.
If i need to, I will probably get 3 5W resistors (gotta determine the value again) to drop the voltage down to 12V. Other than that, i should be able to make the projector work once more, if not better than before.

Oh, these are the <a rel="nofollow" href="http://ledsupply.com/buckpuck.php">http://ledsupply.com/buckpuck.php</a> which run at 1000ma output, and I got the ones that were prewired, but do not have a dimmer since i do not need it in this case.<br/>

Nice, I used my Ryobi batteries all the time for projects - like <a rel="nofollow" href="http://www.instructables.com/id/Homebrew_Remote_Control_Hover_Craft/">this</a><br/>

i'm just wondering... with a lot of 12V 1.0A 10W warm-white 600 lumens LED making it ways to international market from China, is it possible to imitate your rig and attach it to my motorcycle and replace its 12V 1.25A 25/35W halogen bulb?
Or more importantly, are the figures advertised realistic?
BTW, The stock headlight is not bright enough for cloudy dark night on dark street, and your creation seems marvelous...

Yes, I think LED automotive headlights would be great. In fact I'm planning on replacing my car's headlights with LEDs. There's a trick though with automotive lights - legality... You are much more likely to get pulled over by the police for having improper headlights on a motorcycle or car than on a bicycle. So keep that in mind. In any case, be very careful about how you choose the lenses or optics you plan on using, and to make sure you have sufficient cooling. Do it and post your results here!

thanks for the vote of confidence but my main concern would be the ability of the battery and/or engine to keep up with the electrical requirements. Having no experience with electricity in practice (and i did flunk physics!), I'm afraid i might blow up the 12V 3Ah acid-lead battery! or stall the 110 c.c engine.
About legality, over here in Malaysia, we don't have the luminence value of headlights written down, or what type of illumination we use for that matter, so that's not a big problem: unless it's HID/Xenon bulb in non-xenon/HID calibrated headlights which is illegal.
So, I plan to fit the LED assembly into the stock headlight assembly, hoping it won't blind anybody... and make holes for some air.
But the electrical supply issue bugs me. Big time.

Ahh okay. So first of all, my light draws somewhere around 20 watts. If you are using a 25 watt halogen bulb, this should present no problem. You should also get more light, and in a more visible (to other drivers) spectrum of light. So yes, you have plenty of power from your alternator, and the only extra thing to consider is the quality of that power. A halogen bulb is very tolerant of momentary spikes in voltage, but a delicate switching current driver like the one I use may not be. So I would encourage a bit of work in making sure you have clean voltage source (EMI filtering, reverse protection diodes, etc.)
I believe that here in the US the issue is more about the aiming of light rather than its total luminance. The HID/Xenon issue is the same here, because of the aiming. Some of the aftermarket HID/Xenon lights are driving lights or fog lights and others are just HID bulbs made to fit standard housings. In either case, they generally don't confine the beam as well as properly projector beam headlights do. If I can figure out a way to shape the beam well, I'm going to retrofit my car with LEDs.

I'm sorry, but I'm not quite sure what you mean when you say "Bare aluminum is not as good a conductor as one might think." Do you think you could explain this a little further? As it is currently worded, this is a deeply misguided statement.

If you aren't quite sure, how sure are you that it's deeply misguided? :)<br/><br/>Anyway, a polished, or smooth aluminum heat sink will dissipate heat poorly compared to a heat sink where the surface is anodized, painted, or otherwise roughed up. Of course if you paint it with an inch thick of rubber that no longer holds true. The point is that aluminum when machined as I did, comes out pretty shiny and giving it certain coatings will help the aluminum dissipate heat better. So maybe the word &quot;conduct&quot; was inappropriate.<br/><br/><a rel="nofollow" href="http://www.aavidthermalloy.com/products/extrusion/anodize.shtml">effect of anodizing</a><br/><br/>Here's a table I found for thermal emissivity:<br/>Polished aluminium 0.05<br/>Polished copper 0.07<br/>Rolled sheet steel 0.66<br/>Oxidised copper 0.70<br/>Black anodised Al 0.70<br/>Black enamel 0.85<br/>Dark varnish 0.89<br/>Black oil paint 0.92<br/><br/>I suppose I would hae been better off with a thin flat black coating. <br/>

this is because dark surfaces radiate heat far more effectively than a shiny surface. its stated in one of the laws of thermodynamics, but i hate physics, so im not going loking for it :P
i cannot understand why people dont paint their radiators matt black. far more efficiant than white.

So the inverse of Solar radiation is happening, where Black absorbs more solar heat than shiny or white surfaces. I never considered the reverse to be true, very cool thing to know.
thanks!

Right, but in this case it is not a strong mode of heat transfer. You're better off leaving the aluminum uncoated.

how many car driver was blinded and killed ?

the world may never know...

And even if we did know... who says less car drivers is bad! haha. I jest...... maybe.

that inspires deep thought on my part...

On a related note, I was thinking of making a bike-mounted harpoon launcher.

I don't think you need a stipulation in some local code to cover this, this just falls under the header 'reckless endangerment', and not just other people by the light but also yourself from the reaction people might show, there's a good change someone takes matter into their own hands without consulting brightness regulation websites and you should take that into consideration too.

The headlight has a brightness control knob. I use it constantly. I try to be courteous to drivers. Where I ride, there is plenty of ambient light and while the light would be truly blinding in a very dark place, its not nearly so bad in the city on well lit roads.

overkill
but well done(if only i had 150 dollers and a bike)

Why do you need this. the point is for people to SEE you, not be blinded by you...

yes but its also for them to see the road themselves....if there are no cars around then brightness can be increased so there is less strain on the eyes while riding

Congrats on the win!

This is without question the king of all bike light builds. I have seen people use MORE lights, and even car headlamps, but this offers the bst of everything. I suspect that this light is actually illegally bright, which is about the best thing you can say about a home brew project. Cheers for over-engineering.
Also, I'd love a tail light demo photo, akin to the head light demo photo, just for reference.

Where would I get info about what constitutes "illegally bright"? I love this concept.

I tried looking through the California DMV's web site and could not find anything about the specifics of bicycle headlights. Maybe the US DOT has regulations governing them. I know there are regulations pertaining to headlights, turn signals, etc., for cars, but I have not found anything about bicycle headlights. The first night I was using this headlight though I was coming up the final hill and since there were no cars I turned it up to full brightness. It was just at that moment that a police car crested the hill and was coming towards me. He didn't stop me so I guess it isn't THAT illegal. Or maybe he didn't know what section of the VC to apply :)

Any restrictions on the brightness of car headlights will be applicable to any vehicle that is road legal, including a bicycle. You might have gotten lucky with that cop, or he may have not considered it to be to bright, or maybe he was just to awed by the insane ingenuity of this instructable that he couldn't possibly ticket you!

<em>awed by the insane ingenuity of this instructable that he couldn't possibly ticket you</em><br/><br/>That's my feeling. Unless you're actually endangering people with how it's aimed, the cops are probably just gonna smile and shake their heads. And I doubt they carry photometric equipment in their cars! It'd be a hassle to issue.<br/><br/>If anyone DOES get such a ticket for this, please scan it, redact the personal parts, and post it! I'd frame the thing for my wall.<br/>

if its aimed sleightly down and to the right it shouldnt cause a prob for oncoming drivers and your too slow on a bicycle to cause a problem in the rear view of drivers ahead of you even if its not aimed correctly.

Well, I worked for a scooter importer for a while, and there were a whole series of regulations covering every aspect of any vehicle allowed on public roads, I suspect this is a state-by-state issues, but I know there is a maximum allowable luminosity for car headlamps, and this bike light is decidedly above high intensity car headlamps. I would probably look at the NHSA (National Highway Safety Admin). or possibly to the NYSB (National Transportation Safety Board) for these regulations- I know they exist and they probably have to do with luminosity, color and height from the ground.

Cops get mad at my Cold cathodes, its funny.

Wow... umm this is pretty intense
Great job!

Thermal emissivity only applies to radiant heat. In this situation, radiant heat is going to be negligible compared to forced convection. The properties you want to be looking at are surface area and thermal *conductivity*, not thermal emissivity.
You're right that it is preferable to increase the turbulence across the surface of the housing, but it is HIGHLY unlikely that you'll be able to coat the surface of the housing with something that can increase radiant heat and keep the convective heat constant.
Anodizing won't help either. When you anodize, you're coating the surface of the aluminum with a (relatively) thick layer or aluminum oxide. This also doesn't conduct heat as well as pure aluminum (or 6061 aluminum, which is probably what you're using.) The result will be that you're actually insulating the aluminum from convective heat transfer.
The important thing to keep in mind is that you're not radiating much heat. You're going to get several orders of magnitude more heat transfer from forced convection. If you want to increase the heat transfer, try to maximize your surface area.

Yes, you are correct. Now here's a question (because I honestly don't know)... At a microscopic level what is the mechanism of heat exchange during convection? Molecules of the cool air (while in their convection cycle) get in close proximity to the heatsink, or even touch, but what imparts the thermal energy from the hot heat sink to the air? Is it direct contact (conduction)? Is it microscopic radiant heat exchange? In any case you do need excellent conduction of heat to that interface surface, but what goes on at that boundary in convective heat exchange? Also, as you said, increasing the surface area is important. From the perspective of a surface, a polished surface has the smallest possible surface area. Anodizing chemically etches the surface and results in a larger surface area. By how much I don't know.
Finally there's the issue of material longevity. Bare aluminum will form an oxide on its own, and eventually that oxide can (depending on the alloy) get thick, thicker than an anodized surface which I believe will stop the oxide growth to some extent.

It's actually a very complicated issue, and we're actually getting into some basic fluid mechanics. On a very, very small scale (think atoms), the interface between the air and aluminum is what's called a &quot;no slip condition&quot; (http://en.wikipedia.org/wiki/No-slip_condition). In this small region, the air acts as a conductor, not as a convector. As you move away from the surface of the aluminum, the atoms begin to move more and more, and the collision of molecules transfers the kinetic energy of heat through convection. You need good conduction to have good convection. <br/><br/>There are three forms of heat transfer: convection, conduction, and radiation. Materials which are transparent to infrared, like air, do not absorb or emit radiation. Thus, you would not have microscopic radiant heat between molecules.<br/><br/>Aluminum is EXTREMELY reactive with oxygen. It's virtually impossible to expose a piece of aluminum to the atmosphere without it immediately forming a thin film of aluminum oxide. If you scratch the surface of that film, the surface of the scratch will immediately form an aluminum oxide film. Once the film has formed, it doesn't spread down any farther through the aluminum. The entire purpose of aluminum anodization (other than the obvious aesthetic one) is to increase the thickness of this layer to an unnatural thickness. I think what you're thinking of is a 3000 series aluminum, which has pretty poor oxidation properties, and tends to get some white scale on it when it's left outside. 95 times out of 100, you'll be a 6061 or 6063 aluminum to make your housing, and this won't be an issue.<br/><br/>You will find that chemically etching the metal, as in anodizing, will not give you a measurable increase in heat transfer. Try to put thermal fins (like a CPU heat sink) on the body, or better yet, try to improve the thermal interface between the heat source and heat sink. Thermal greases usually outperform epoxies, so you might want to use a mechanical fastener to physically attach the LEDs, and a thermal grease to actually transfer the heat.<br/><br/>Coating or anodizing an aluminum housing *will* decrease the amount of heat transfer from this application. Perhaps not a significant amount, but it should be made clear that coating the housing is not that important. Especially from a functional standpoint.<br/>